The present invention relates to methods of making enhanced efficacy antiperspirant salts and particularly stabilized solutions of such salts.
Enhanced efficacy aluminum and aluminum-zirconium antiperspirant salts are well known and are described, for example, in GB 2,048,229, EP 405,598, U.S. Pat. No. 4,359,456, U.S. Pat. No. 4,775,528, U.S. Pat No. 4,859,446, U.S. Pat. No. 4,871,525, U.S. Pat. No. 4,900,534, U.S. Pat. No. 4,944,933, U.S. Pat. No. 5,202,115, U.S. Pat. No. 5,234,677, U.S. Pat. No. 5,296,623, U.S. Pat. No. 5,330,751 and U.S. Pat. No. 5,356,609. These enhanced salts are also known to rapidly revert back to their non-enhanced state (for example, as evidenced by an HPLC peak 4 to peak 3 area ratio of 0.3 or less) in aqueous solution, particularly at concentrations greater than 20%. Consequently, the enhanced antiperspirant salts are generally only available in powder form.
A preferred method of preparing enhanced efficacy antiperspirant salts comprises heating a 5 to 18% aqueous solution of aluminum salt, preferably aluminum chlorohydrate, at a sufficient temperature and for a sufficient time to provide an HPLC peak 4 to peak 3 area ratio of at least 0.5, preferably at least 0.7, and most preferably at least 0.9, with at least 70% of the aluminum contained in said peaks. The aqueous solution may be obtained by diluting a standard commercially available 50% salt solution with water to the desired concentration, which is preferably 8 to 15%. The temperature and time of heating may be adjusted as necessary to achieve the desired degree of conversion to the enhanced state. Generally, longer times are required at lower temperatures. It is preferred to heat above 50.degree. C., more preferably at 70.degree. to 100.degree. C., for at least two hours, more preferably for at least 10 hours or more. Excellent results are obtained by heating at about 80.degree. to 85.degree. C. for about 15 to 20 hours.
An alternative method of preparing aqueous solutions of enhanced efficacy aluminum hydroxy halides is that described in U.S. Pat. No. 4,859,446 and U.S. Pat. No. 5,356,609, the disclosures of which are incorporated herein by reference. In this method aluminum metal is reacted with aluminum halide, typically aluminum chloride, or with hydrogen halide, typically hydrochloric acid, in water at a temperature of about 50.degree. to 100.degree. C., the concentration of the reactants being such as to provide an aqueous solution of aluminum hydroxy halide, typically aluminum chlorohydrate, of about 5 to 25%, preferably about 8 to about 15%, by weight.
A number of references describe various ways of making alcohol soluble antiperspirant actives. These references include, for example, U.S. Pat. No. 3,405,153, U.S. Pat. No. 3,420,932, U.S. Pat. No. 3,523,130, and U.S. Pat. No. 3,947,556. In each case concentrated solutions of the antiperspirant active (i.e., in the 40 to 50% range) are employed as a starting material and the product is obtained as a powder, which must then be redissolved in the desired alcohol solution. Such techniques pre-date the availability of enhanced efficacy salts and are not believed to be applicable thereto as they would likely cause reversion to the non-enhanced state. In EP 7191 there is exemplified a process for making a spray dried, powdered complex of enhanced aluminum chlorohydrate and propylene glycol, which complex may then be dissolved in alcohol.
Two methods of making polyhydric alcohol solutions of antiperspirant salts are described in EP 295,070 and EP 404,533. In these methods a powdered antiperspirant salt, which may be an enhanced efficacy salt, is dissolved directly in a polyhydric alcohol, such as propylene glycol. In the former case, the polyhydric alcohol contains about 10 to 20% water. In the latter case, the antiperspirant salt has a water content greater than 10%.
A method of making polyhydric alcohol solutions of antiperspirant salts which are free of unbound water is described in U.S. Pat. No. 4,781,917. In that method, a powdered antiperspirant salt, which may be an enhanced efficacy salt, is dissolved in water (a 50% solution is exemplified), a polyhydric alcohol, such as propylene glycol, is added to the aqueous solution, then all of the water is removed by heating under vacuum. In U.S. Pat. No. 5,463,098, example 21 describes a method of making a propylene glycol solution of an aluminum-zirconium antiperspirant salt neutralized with zinc glycinate. An aqeous solution of aluminum chlorohydrate is refluxed in the presence of a small amount of propylene glycol, the solution is cooled to 70.degree. C., zirconyl hydroxychloridegly is added, the solution is cooled to 40.degree. C., then zinc glycinate followed by propylene glycol is added. This solution is then distilled under vacuum to remove water, leaving a 30% by weight solution of antiperspirant active in propylene glycol. Other examples describe spray drying the product in order to recover the powdered antiperspirant active, which is said to be soluble in liquid diols.
In WO 96/14052 there is disclosed a process of preparing a solution of an enhanced efficacy aluminum antiperspirant salt in a polyhydric alcohol by (a) providing an aqueous solution consisting essentially of about 5% to about 20% by weight of an enhanced efficacy aluminum antiperspirant salt in water, the enhanced efficacy aluminum antiperspirant salt having been prepared in situ without having been dried to a solid powder; (b) mixing the aqueous solution with a sufficient amount of a liquid polyhydric alcohol (e.g. propylene glycol) to provide a mixed solution which has an antiperspirant salt to polyhydric alcohol ratio of about 1:4 to about 1.2:1; and (c) rapidly evaporating the water from the mixed solution under vacuum to provide a liquid polyhydric alcohol solution containing about 20 to 50% enhanced efficacy aluminum antiperspirant salt and about 2 to 16% water, with the balance being said polyhydric alcohol. When an aluminum-zirconium complex is desired in the final product, the zirconium salt can be added at any stage prior to the evaporation step (c). If the water content exceeds 16%, the peak 4 to 3 ratio of the salt will deteriorate on storage.